Process for improving the creep resistance in rayon industrial yarns,cords and the like



United States Patent PROCESS FOR IMPROVING THE CREEP RESIST- ANCE IN RAYON INDUSTRIAL YARNS, CORDS AND THE LIKE Johannes J. Van Heuvelen, Arnhem, Netherlands, as-

signor to American Enlta Corporation, Enka, N.C., a corporation of Delaware No Drawing. Filed Sept. 15, 1965, Ser. No. 487,632 Claims priority, application Netherlands, Sept. 18, 1964,

6410884 U.S. Cl. 8-116 2 Claims Int. Cl. D06m 11/04, 1/02 ABSTRACT OF THE DISCLOSURE This invention relates to a process for the improvement of the properties of industrial yarns and cords of regenerated cellulose, especially those yarns used to produce tire cord. More particularly, the invention relates to a process which reduces the creep occurring in tire cord made of regenerated cellulose.

Industrial yarns and cords made of regenerated cellulose are well known for use in reinforcing rubber products such as automotive tires, belting, webbing, etc. Rubber products incorporating such yarns and cords are subjected to forces which extend the rubber during normal use. Such extension is particularly detrimental to reinforcing yarns and cords of regenerated cellulose and quite often causes an extension in the yarn in excess of the normal extension which occurs under load conditions. This over-extension produces in the yarn a phenomenon known as creep which is irreversible. The permanent increase in the length of yarn quite often gives rise to the formation of cracks in the rubber, thus deteriorating the quality of the rubber product.

It is known to improve the tensile strength and fatigue resistance of cotton tire cord by treatment of the cord with an aqueous solution having a controlled pH and containing an electrolyte composed of a cation of a strong base and an inorganic anion. U.S. Patent 2,346,126 describes a process for increasing fatigue resistance in cotton tire cord by treating cotton yarns with an aqueous borate solution having a pH between 8 and 13 and sub sequently twisting the yarns, while still wet, to form a tire cord. Such a treatment increases the fatigue resistance of the tire cord and does not adversely affect the tensile strength thereof. However when such a process is applied to industrial yarns of regenerated cellulose, i.e. rayon, the tensile strength of the yarns and cords is greatly reduced, making the process unacceptable for commercial products.

It is an object of the present invention to provide a novel solution for treatment of regenerated cellulose yarn and cord produced therefrom to improve its resistance to creep, without adversely affecting the tensile strength thereof. a

It is another object of this invention to provide an improved process for the treatment of regenerated cellulose yarns and cords which require a low creep factor and high tensile strength.

3,425,787 Patented Feb. 4, 1969 It is a further object of this invention to provide an improved regenerated cellulose industrial yarn product having high strength and high resistance to creep.

These and other objects of the invention will become apparent from the following detailed description and examples.

According to the present invention, the creep which occurs during normal use of industrial yarns and cords of regenerated cellulose can be reduce-d by treating these yarns with an aqueous solution of 0-.3-3. 0% borax, by weight, which solution is maintained within a pH range of 6.5-7.7 by the addition of a buffer. It has been found that industrial yarns and cords treated with such a solution show a marked decrease in creep over previously known regenerated cellulose yarns, without consequent loss in their tensile strength.

It has been discovered that if the regenerated cellulose yarns and cords are treated with solutions containing less than 0.3% by weight of borax, no appreciable reduction in creep can be noted. If the borax concentration is higher than 3% by weight, the adhesion of industrial yarn and cord to rubber is unfavorably influenced and the tensile strength of the yarn and cord is reduced. For optimum conditions, it has been found that solutions containing (LS-0.7% by weight of borax are to be used.

If the pH of the borax solution is lower than 6.5 or higher than 7.7 during the process, the tensile strength of the industrial yarns and cords is considerably reduced.

The yarns and cords can be treated either wet or dry without appreciable difference in result. The yarns and cords can be treated with the borax solution while they are traveling, or after collection on a spool or in the form of a spinning cake. Although the yarns and cords can be treated either wet or dry, better results are obtained in tensile strength if the yarns and cords are treated while Wet and without having undergone a drying treatment in any one of the preceding process steps, i.e., while they are in gel state.

During treatment with the borax solution, the yarns may be stretched; however, it is preferred that during treatment their length be kept constant. Also, best results can be obtained if the wet yarns are heated while they are in the gel state.

Various buffers may be used to control the pH of the aqueous solution. Some of the suitable buffers are primary and secondary sodium phosphate, trihydroxymethyl aminomethane (tris butter), triethanolamine, maleic acid, and boric acid. It is preferred to use boric acid.

During the normal continuous process of manufacturing industrial yarns of regenerated cellulose, freshly spun yarns are decomposed, stretched, washed and dried. Between the washing and drying steps the: yarns are usually treated with a liquid containing one or more finishes and water. The finishing liquid may be applied to the yarns by passing the yarns through a bath or by spraying the finish directly onto the yarn. Although the yarns may be treated at any point in the process after regeneration with the borax solution of the present invention, it is especially convenient to treat the yarns with the boraxcontaining solution by adding the solution to the finishing liquid. If necessary, the borax treated yarn may be stretched, with stretching taking place during or after passing the yarns through the finishing liquid. As previously mentioned, the process is also etfectively carried out while maintaining the yarn in unstretched condition during and after the borax application.

In addition to buffers, the borax solution may contain other compounds, such as Wetting agents, agents that improve adhesion to rubber, or agents that improve resistance to heat and light, without affecting the quality of the product.

Industrial yarns of the present invention can be treated with the borax solution either in the twisted or untwisted state and twisting may be carried out on either wet or dry yarns without affecting the product quality. It is also possible to effectively treat corded yarns without detracting from the product. The invention will be further described must be maintained within a range of 6.5-7.7 to prevent appreciable loss in tensile strength of the cord.

EXAMPLE III Run 14 was carried out in the same manner described and understood by means of the following examples, in Example 1, except that after Washlng, e Yf Was which are not intended to limit the invention dried. The dry yarn was passed through a fil'llShlllg bath containing 0.7% by weight of borax. The pH of the bath EXAMPLE I was maintained at 7.5by addition of boric acid. The yarn Eight runs were madtl- In 11111 1, a Control, freshly was corded as in Example I and the bone dry strength p 1,000 filament rayon y having a denier Of 1,650 was 18.0 kg. Cord creep was determined to be 1.0%. Was decomposed, Stretched and Washed in a continuous Example III indicates that drying the yarn prior to treatp The control Y Was then P through a ment with the borax bath does not affect the improved refinishing hath containing Watfif and finish having 3 P sults in creep obtained by use of the borax solution. of 7.5. The yarn was dried on a drum.

In runs 2-8, yarns prepared as the control were sub- EXAMPLE IV jected to varying amounts of borax in the finishing bath. Run 15 was carried out in the same manner as described The finishing bath was maintained at a pH value of 7.5 in Example 1, except that the pH of the finishing bath, by the addition of boric acid. containing 0.7% by weight of borax, was maintained at The yarns of runs 18 were Z twisted to 472 turns per a value of 7.5. meter and made into a tire cord by twisting two of such Run 16 was made under the same conditions as run 15, yarns into a cord having an S twist of 472 turns per meter. except that the finishing bath contained no finishing agent. The cords prepared were tested for creep and tensile The yarns of runs 15 and 16 were not twisted into cords, strength. but tensile strength and the creep were measured directly Creep was determined in the following manner. A preon the yarns. The results of these measurements are pared cord, which had been treated with a latex emulsion shown in Table 3. and dried at 150 C., was heated at 150 C. for 90 seconds TABLE 3 while being maintained at constant length. A length of Run this cord, a (in cm.) was loaded at 140 C. with a weight of 2.2 kg. The extended cord was measured after 2 15 16 minutes, length 17, and 120 minutes, length c. The percent- 0.7% by weight 0.7% by weight age of creep was then calculated by formula igg gfg gfgigi cb 7x100 83$? i fi r( if% i i i i t3 133 r The results of these measurements are represented in A comparison of h creep values i d i Example Table 1. IV with the creep value of the untreated yarn indicates TABLE 1 Run No.

(con trol) 3 4 5 6 7 8 Percent by weight borax 0 0. 1 0 3 0.5 0. 7 1 3 4 Bone dry tensile strength, in kg. 18.5 18.6 18 5 18.5 18.6 13,3 13,1 17,0 Creep, in percent- 1.4 1.4 1 2 1.1 0,3 Q6 (16 It has been found that a 10% reduction in Creep from that the borax treatment of the present invention is not original creep values prevents formation of cracks in the d d t upon h use f a fi i hi againrubber. From Table 1, it can be seen that the cord creep decreases by addition of at least 0.3% by weight EXAMPLE V of borax to the finishing liquid. However, the tensile In run 17, rayon tire cord, prepared as in Example I, strength of the cord is reduced if the borax concentration having a bone dry tensile strength of 18.5 kg. and a creep is 4%, thus indicating that a concentration no higher than 3% is preferred.

EXAMPLE II Runs 9-13 were carried out in the same manner as indicated in Example I with the exception that the finishing liquid contained 0.7% by weight of borax for all runs.

In run 9, the pH of the finishing liquid was maintained at a value of 5.5 by addition of a butter of Na HPO and KH PO In runs 10-12, pH values of 6.5, 7.7, and 8.0, respectively, were maintained by the addition of a butter of boric acid. In run No. 13, the finishing liquid, which did not contain a buffer, had a pH of 9.5. The yarns were made into cords as in Example I and the tensile strength and creep of these cords were measured. The results are shown in Table 2.

The results of Table 2 indicate that by the addition of borax, cord creep, which was originally 1.4% (Run 1, Example I), decreases to an average value of about 1.0%. However Table 2 indicates that the pH of the borax bath of 1.4%, was passed through a bath which contained water and 0.7% by weight of borax. The bath was maintained at a pH of 7.5 by the addition of boric acid. After the cord had been treated, it was dried and was found to have a bone dry tensile strength of 18.5 kg. and a creep of 1.1%.

The results of Example V indicate that the invention is not limited to application of the borax solution to regenerated cellulose yarn, but the solution may be applied with equal success to the regenerated cellulose cord.

EXAMPLE VI Runs 18-20 were carried out in the same manner as described in Example I, with the exception that the borax content of the finishing liquid was maintained at 0.7 by weight.

In these runs, respective use of trihydroxymethyl aminomethane, triethanolamine, and maleic acid brought the pH values of the baths to 7.3, 7.1, and 6.7, respectively. The yarns were corded as in Example I and their tensile strength and creep are indicated in Table 4.

TABLE 4 Run N o 18 19 2O Bone dry tensile strength, in kg 18. 6 18. 5 18. 4

Creep, in percent 1. 0 0. 9 1. 0

Example VI indicates that the pH of the borax baths can be maintained at desired values not only with borax acid, but with other buffer compounds.

While specific examples of preferred methods embodying the present invention have been described above, it Will be apparent that many changes and modifications may be made therein without departing from the spirit of the invention. It is therefore understood that the examples cited and the methods of procedure set forth are intended to be illustrative only, and are not intended to limit the 10 aminomethane, triethanolamine, maleic acid and boric acid.

2. A method as defined in claim 1 in which the buflier is boric acid.

References Cited UNITED STATES PATENTS 2,346,126 4/1944 Lessig et a1. 8116 X 2,644,765 7/1953 Frisch et a1. 252 351 X 2,838,455 6/1958 Tompkins 252--8.6

FOREIGN PATENTS 940,270 10/ 1963 Great Britain.

OTHER REFERENCES Marsh: An Introduction to Textile Finishing, second edition, published 1948 by Chapman & Hall Ltd. of Lon don, England, pp. 524-529.

HERBERT B. GUYNN, Primary Examiner.

US. Cl. X.R.

57153; Ill-139.5, 144; 252- 86 

